用于顺序文件写入的posix_fadvise()参数是什么? [英] What posix_fadvise() args for sequential file write?

问题描述

我正在开发一个按顺序写一个大文件(根本不读)的应用程序，并且我想使用posix_fadvise()优化文件系统的行为.

I am working on an application which does sequentially write a large file (and does not read at all), and I would like to use posix_fadvise() to optimize the filesystem behavior.

联机帮助页中的功能描述建议最合适的策略是POSIX_FADV_SEQUENTIAL.但是，Linux实现描述怀疑:

The function description in the manpage suggests that the most appropriate strategy would be POSIX_FADV_SEQUENTIAL. However, the Linux implementation description doubts that:

在Linux中，POSIX_FADV_NORMAL将预读窗口设置为备用设备的默认大小； POSIX_FADV_SEQUENTIAL将该大小加倍，并且POSIX_FADV_RANDOM完全禁用文件预读.

Under Linux, POSIX_FADV_NORMAL sets the readahead window to the default size for the backing device; POSIX_FADV_SEQUENTIAL doubles this size, and POSIX_FADV_RANDOM disables file readahead entirely.

由于我只写数据(也可能覆盖文件)，所以我不希望有任何预读.然后我应该坚持使用POSIX_FADV_SEQUENTIAL还是使用POSIX_FADV_RANDOM禁用它?

As I'm only writing data (overwriting files possibly too), I don't expect any readahead. Should I then stick with my POSIX_FADV_SEQUENTIAL or rather use POSIX_FADV_RANDOM to disable it?

其他选项(例如POSIX_FADV_NOREUSE)如何?还是根本不使用posix_fadvise()进行书写?

How about other options, such as POSIX_FADV_NOREUSE? Or maybe do not use posix_fadvise() for writing at all?

推荐答案

这全都取决于数据的时间局部性.如果应用程序在写入后不久就不需要数据，则可以使用POSIX_FADV_NOREUSE避免写入缓冲区缓存(与open()中的O_DIRECT标志类似).

It all depends on the temporal locality of your data. If your application won't need the data soon after it was written, then you can go with POSIX_FADV_NOREUSE to avoid writing to the buffer cache (in a similar way as the O_DIRECT flag from open()).

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